The control circuitry for a data storage device such as a magnetic disc drive typically resides on discrete chips mounted on a printed circuit board fastened to the underside of the disc drive. There is a trend in data storage device development to make the devices smaller while maintaining or increasing the device storage capacity. Recently, this trend as lead to the incorporation of most if not all of the circuitry and control systems previously found on the printed circuit board into a single integrated circuit known as a SOC (System On a Chip). The SOC incorporates several discrete devices on a single silicon substrate. This configuration can improve performance, reduce cost, and reduce power consumption.
However, there is a serious drawback to such configurations. Previously visible device input/output (IO) pads are no longer visible making testing very difficult or impossible. In the case of a data storage device such as a magnetic, or magneto-optical disc drive controller with an embedded read/write channel in an SOC, the controller/channel interface is no longer visible or directly controllable. The Non Return to Zero (NRZ) data bus between the controller and the channel, in particular, makes testing of the controller in a standalone manner impossible. Attempts to test the controller logic via the internal channel are very difficult, time consuming, and expensive.
Accordingly there is a need for providing a simple mechanism in a data storage device that has an integrated read/write channel control to permit testing of controller functions. The present invention provides a solution to this and other problems, and offers other advantages over the prior art.